1. Field of the Invention
The invention relates to a machine tool and more particularly to a machine tool for cutting workpieces.
2. Background Discussion
In conventional machine tools for cutting workpieces the relative movement between the tool and the workpiece required for multi-axis machining is generally enabled by three machine parts which are, relative to each other, linearly shiftable along the main coordinate axes. In European patent publication 721819, for example, a machine tool is described in which a machining unit formed as a vertical milling head is disposed on a machine tool table so as to be shiftable, by means of a compound slide, in two horizontal axes which are perpendicular to each other. The compound slide consists of a cross slide shiftable on the machine tool table on first guide rails, a longitudinal slide being shiftable on the cross slide on second guide rails. For the feeding movements along the vertical axis the milling head is disposed on the longitudinal slide so as to be vertically shiftable on third guide rails. In machine tools designed in this way separate linear guides are required for each of the three machine parts shiftable along one of the main coordinate axes, respectively. These are, however, of a complex design and require correspondingly high investment and installation costs. Above that the masses to be moved along the respective coordinate axes are usually relatively large in such machines, whereby the moving speed of the machining unit is limited and the requirements to the guides and drives are correspondingly high.
In German patent publication 19806085 a machine tool for machining workpieces in three axes is described in which one slide, respectively, is shiftable in guides on the two transverse beams of the frame-shaped machine tool table. A coupling system formed by swivel arms connects each of the two slides to a machining unit comprising another slide as well as a tool head shiftable therewith. By controlled movements of the two slides on the longitudinal sleepers the machining unit can be moved to any position within a square machining area. In certain positions of the machining unit, however, extremely high loads are applied on the coupling to system in corresponding angular positions of the swivel arms so that this machine tool is not suitable for high loads, for example, during roughing-down work with a high cutting performance.
Accordingly, there is a need for a machine tool that is relatively fast and stable. The present invention satisfies these needs and provides related advantages as well.
It is a primary purpose of the invention to provide a machine tool enabling fast machining, including an accurate and rapid positioning of the machining unit with a stable construction including as few linear guides as possible.
According to the invention the purpose is met in that the tool slide comprises a transverse support slidably guided on/along the machine tool table and includes two cross slides shiftable in its longitudinal direction by means of a motor, the working unit being jointedly disposed between the cross slides for enabling an axial movement of the work spindle by means of a coupling mechanism comprising at least two dimensionally stable swivel arms.
The machine concept of the invention is characterized by an extremely stiff machine design of simple construction that enables highly dynamic and at the same time highly accurate shifting movements. With the transverse support shiftable along a first coordinate axis on or along the machine tool table, and with a simple movement of the two cross slides along a second coordinate axis, a fast and accurate positioning of the working unit in space is obtainable with the coupling mechanism of simple construction comprising low movable masses. The cross slides can also be light and simple so that rapid movements and high accelerations are possible. Another important advantage of the machine tool according to the invention is that only one guide is required for shifting movements in two axes.
In a machine tool having a gantry construction, for example, the transverse support may be arranged on two lateral portions of a machine tool table so as to be horizontally shiftable. The transverse support, however, may also be guided along a front or side wall of a machine tool table so as to be vertically movable. In both embodiments a rapid axial movement of the work spindle or work spindles is obtainable by means of the coupling mechanism.
In an embodiment of efficient design the coupling mechanism comprises, for example, two swivel arms, the one ends of which are respectively hinged to a cross slide, and the other ends of which are respectively hinged to the opposed sides of the machining unit. Adjacent to one of the two swivel arms another swivel arm is provided by which the machining unit is jointedly connected with one of the cross slides. In this way a kind of parallel rod or shearing kinematics is obtained which enables an axial movement of the work spindle in case of a synchronous movement of the cross slides in opposite directions, and also enables a movement of the work spindle transverse to their axial direction in case of a synchronous movement of the cross slides in the same direction.
In a light weight and yet stable embodiment the swivel arms may, for example, be jointed beams welded from side plates and transverse braces. The swivel arms may also be formed as supports or the like having a circular or rectangular cross-section.
Another advantageous embodiment is characterized in that the length of at least the upper swivel arm is adjustable. In this way an inclined posture of the machining unit is enabled whereby, for example, shaped bevels or the like can be machined in a simple way. The rapid and suitable automatic length adjustment of a swivel arm may be realized by designing the same as a telescope arm comprising inner and outer arm portions which are shiftable with respect to each other. The movement of the arm portions may be effected by linear drives or other suitable drives in this case.
Another possibility to obtain an inclined posture of the machining unit is to provide at least one of the two cross slides with a first slide part horizontally shiftable on the transverse support and a motor-driven second slide part slidably guided on the same on guide rails. The upper end of the upper swivel arm is hinged to the second slide part. In this way a tilted or inclined posture of the machining unit may be obtained even without swivel arms with adjustable lengths.
In an embodiment particularly suitable for a rapid machining of small to medium-sized workpieces, the workpiece support comprises a support column turnable about a vertical axis by means of a motor, clamping blocks or the like arranged in equal intervals in the circumferential direction being attached to the support column so as to be turnable about its central axis. Thereby a rapid workpiece exchange is enabled without excessive standstill times. For machining large and heavy workpieces, the workpiece support may, however, also be a rigid round table or a round table rotatable about a vertical axis.
A rapid tool exchange may be realized in a particularly advantageous manner by providing a tool storage means comprising at least two opposed tool magazines disposed in the rear part of the machine tool table. For a tool exchange the machining unit may be moved between the two tool magazines, in which case then the old tools may be disposed in one magazine and the new tools taken from the opposite magazine with minimum moving distances.
In a particularly efficacious embodiment, the machining spindle comprises two or more work spindles. In this way several workpieces may be processed simultaneously.